A prospective study of physical activity and risk of prostate cancer in USphysicians

Background Exercise can suppress androgen production and may thus decrease the risk of prostate cancer. However, findings from epidemiological studies assessing physical activity and risk of prostate cancer are inconsistent. Methods We prospectively examined the association between physical activity and prostate cancer risk in the Physicians' Health Study (PHS), a randomiz ed trial of low-dose aspirin and beta-carotene among 22 071 men aged 40-84 without self-reported myocardial infarction, stroke and cancer. At baseline in 1982, men were asked about the frequency of exercise vigorous enough to work up a sweat. Physical activity was assessed in a similar fashion again at 36 months of follow-up. Results During 11.1 years of follow-up (258 779 person-years), 982 cases of prostate cancer occurred and were confirmed by medical record review. Afte r adjustment for potential confounding factors (including age, height, rand omized treatment assignment, smoking status, alcohol intake, use of multivi tamins, history of diabetes, history of hypertension and history of high ch olesterol), the relative risks for prostate cancer associated with exercise vigorous enough to work up a sweat were 1.0 (referent) for frequency less than once per week, 1.02 (95% CI: 0.82-1.26) for once per week 1.07 (95% CI : 0.90-1.27) for 2-4 times per week and 1.11 (95% CI : 0.90-1.36) for 5+ t imes per week. Across all subgroups of men categorized by age, body mass in dex, smoking status, alcohol intake, use of multivitamins, history of diabe tes, history of hypertension and history of high cholesterol, there were no significant associations between frequency of exercise vigorous enough to work up a sweat and prostate cancer risk. After excluding cases of prostate cancer that occurred during the first 36 months of follow-up, again, there was no significant association. Combining physical activity assessments at baseline and at 36 months also yielded no significant association with pro state cancer risk. Conclusions These observational data from the Physicians' Health Study do n ot support the hypothesis that increased physical activity reduces the risk of prostate cancer.